How often does an O ring on an underwater camera housing need to be replaced if

You should definitely do a caliper measurement on the rubber diameter but the ring diameter measurement will haunt you a bit. Try and keep the ring as concentric as possible while doing a ruler measurement. However, it is critical to get it right or the ring will not remain in the channel.

Olympus is only going to give you there internal part number. In fact the marketing people will be absolutely clueless to the actual manufacturing BOM (Bill of Materials).

On a better note, I should have clarified in my original post that by protecting your O-ring you can easily extend its life beyond possibly a 3 to 5 year period. Yes, that’s an ambiguous value but the rubber is no longer being attacked. That’s also with the consideration that this housing was probably designed for about 4 atmospheres. The fact that you’re only using the housing for rain and snow makes it even that much less a liability because there are no partial pressures to deal with and it may very well last the usefulness of the camera itself.

Regards,

Rick